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BMW E39 Radiator Outlet Temperature Sensor Removal
 
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Pelican Technical Article:

BMW E39 Radiator Outlet Temperature Sensor Removal

Kerry Jonsson

Time:

2 hours2 hrs

Tab:

$35

Talent:

*****

Tools:

DVOM, test leads,

Applicable Models:

BMW 525i Sedan/Wagon (2001-03)
BMW 528i Sedan/Wagon (1997-00)
BMW 530i Sedan (2001-03)
BMW 540i Sedan/Wagon (1997-03)

Parts Required:

Coolant, coolant sensor

Hot Tip:

Keep the radiator cap on so you don't lose too much coolant

Performance Gain:

Prevent check engine light from coming on.

Complementary Modification:

Lower radiator hose

BMW, as well as making the ultimate driving machine, has some of the most sophisticated electronics in the automotive industry. The self-diagnostic features of the car can isolate the system that is not functioning and sometimes why. As an example the cooling system has an electrically assisted thermostat that helps control engine temperatures in a varying range of circumstances. These cars can either sit in traffic on a 100 degree F day or cruise at 65mph on a frigid winter day where cold air cools the coolant in the radiator a lot. Correct engine temperature is required for proper engine mechanical operation and computerized fuel injection operation. To verify the e: thermostat is working, a second coolant temperature sensor is mounted in the radiator lower coolant hose. This sensor helps the DME control unit determine how the e: thermostat is functioning. If the sensor fails it will flag a code and turn on the check engine light. In this tech article we will go over all the steps to check if the sensor is working properly and how to replace it if it is not.

You do not have to drain and refill the system to perform this repair but it is recommended that you do. BMW recommends that you replace your coolant every 2 to 3 years depending on what BMW coolant you use. See our tech article on draining, refilling and bleeding the cooling system.

Outlet Temperature Sensor Testing:

This photo illustrates under the hood of the car on the right side of the radiator.
Figure 1

This photo illustrates under the hood of the car on the right side of the radiator. Locate the radiator outlet temperature sensor in the lower radiator hose where it enters the radiator. It is a two wire sensor.

At the sensor push in on the locking tab (green arrow) in the direction of the blue arrow then unplug the connector by pulling it straight up.
Figure 2

At the sensor push in on the locking tab (green arrow) in the direction of the blue arrow then unplug the connector by pulling it straight up.

With the connector (green arrow) attach one red test lead to one terminal and the black test lead to the other terminal.
Figure 3

With the connector (green arrow) attach one red test lead to one terminal and the black test lead to the other terminal. Turn on the ignition key and you should measure approximately 5.0 volts (red arrow), if not you have a computer or wiring problem. If you measure -5.0 volts you have the leads backwards. Simply reverse the leads.

Plug the connector back in and back probe the two connectors like we did here (green arrow).
Figure 4

Plug the connector back in and back probe the two connectors like we did here (green arrow). Attach the red lead to one terminal and the black lead to the other terminal. With a cold engine (about 60 degrees F) you should read about 4.0 volts. If you read -4.0 volts then simply switch the two leads.

Start the engine and let it idle for 10 to 15 minutes.
Figure 5

Start the engine and let it idle for 10 to 15 minutes. When the thermostat opens this temperature sensor will start to change the signal voltage. The voltage should drop and fluctuate between 1.30 volts and 1.10 volts as the thermostat opens and closes with temperature.

You can measure between the two terminals (green arrow and yellow arrow).
Figure 6

You can measure between the two terminals (green arrow and yellow arrow). The resistance should be about 3000 to 4000 ohms. As the coolant coming out the radiator gets hotter the resistance will drop to a several hundred ohms.

Outlet Temperature Sensor Replacement:
To remove the sensor squeeze the two tabs (green arrows) and pull the sensor straight up in the direction of the blue arrow.
Figure 7

To remove the sensor squeeze the two tabs (green arrows) and pull the sensor straight up in the direction of the blue arrow. Coolant will leak out. If you leave the radiator cap on the cooling system should be in a vacuum if the car is cold and very little coolant should come out. Put a drain pan underneath the car to catch any dripping coolant. Installation is the reverse of the removal steps. Insert the sensor in the same position as the old one and plug the connector in.

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Comments and Suggestions:
Elon Comments: My e39 530D will not reach operating temperature. when i drive the car in city traffic it will climb a but but when i will drive the car on highway speeds at a winter day 35F it will cool down again.

I changed the thermostat but that didn't change anything.
do you have any suggestions?
November 28, 2016
  Followup from the Pelican Staff: Ir does sound like a faulty thermostat. Unless the temp displayed is not correct and the sensor is at fault. - Nick at Pelican Parts  
Todd Comments: My temp goes up to the red when I'm stuck in traffic and/or traveling at low speeds for a period of time and will go down once I have gotten up to around 40mph or like today it just went back down to normal but I was still stuck in traffic and driving slow....I have had this problem for awhile now and I have replaced the water pump, belts, hoses, clamps and the thermostat twice, I have bled the system and my fan clutch is fairly new....scratching my head on this...is there a temperature sensor located somewhere or is there a issue with my radiator??? Please advise
October 27, 2016
  Followup from the Pelican Staff: If it only happens when going slow, the cooling fan or water pump may be at fault. - Nick at Pelican Parts  
freddie Comments: yes one time I gave my car the peddle right befor I turned off the key now when the car gets worm its hard to start I would like to thank you guys for your help an suport
October 6, 2016
  Followup from the Pelican Staff: When your engine doesn’t start you’ll want to check the basics. Check spark, fuel injector pulse and fuel pressure, volume, quality and engine compression. Are there any fault codes? Once you figure out what is missing, it will be easier to diagnose. - Nick at Pelican Parts  
freddie Comments: for a long time my temp gauge would go up an down an now wont work at all can this be the gauge are are could it be a sencer
October 6, 2016
  Followup from the Pelican Staff: If stuck down could be either. Try unplugging the sensor, does it go to full hot? - Nick at Pelican Parts  

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Page last updated: Wed 12/7/2016 02:05:47 AM